1. Field of the Invention
The invention relates to a bus driver for transmitting data signals via wires of a bus, which bus driver comprises:
a first supply terminal and a second supply terminal for the connection of a supply voltage for the bus driver, PA1 a first bus terminal and a second bus terminal for the connection of respective wires of the bus, PA1 a first transistor of a first conductivity type having a first main current path connected between the first supply terminal and the first bus terminal and having a first control electrode, PA1 a second transistor of a second conductivity type opposite to the first conductivity type having a second main current path connected between the second supply terminal and the second bus terminal and having a second control electrode, and PA1 drive means for driving the first control electrode and the second control electrode. PA1 a common node, PA1 a third transistor of the first conductivity type having a third main current path connected between the first supply terminal and the common node and having a third control electrode coupled to the first control electrode, PA1 a fourth transistor of the second conductivity type having a fourth main current path connected between the second supply terminal and the common node and having a fourth control electrode coupled to the second control electrode, PA1 a first control voltage source connected between the third control electrode and the common node, and PA1 a second control voltage source connected between the fourth control electrode and the common node.
2. Description of the Related Art
Such a bus driver is known from European Patent Specification EP 0 576 444 and is used in so-called Controller Area Network (CAN) bus systems which are used, inter alia, in cars. For this, use is made of transceivers (transmitter/receiver), information being transmitted as a differential signal via a two-wire bus having its two wires connected to the first and the second bus terminal. The transmitter supplies data signals to the bus and is from now on referred to as bus driver. The two bus wires are usually referred to as CANH and CANL and are connected to a pull-down resistor and a pull-up resistor at the receiver side. The voltages across the two bus wires have opposite polarities, as a result of which the spurious electromagnetic fields radiated by the two wires cancel one another. In the case of a high degree of symmetry the bus wires can take the form of a twisted pair and no expensive shielding is necessary. For this purpose the symmetry of the signals on the two bus wires should be as high as possible.